Printers that print by synchronizing operation of the printhead in the main scanning direction, and the paper feed operation in the sub-scanning direction, are known from the literature. Such printers that print on both the outbound pass and the return pass of the printhead (print bidirectionally) in order to increase the printing speed are also known. Such bidirectional printing is widely used in color inkjet printers, but the order in which ink is applied differs on the outbound pass and the return pass due to the arrangement of the nozzle rows for each color, and differences in color between the outbound pass and the return pass can therefore result.
To address this problem, JP-A-2007-136845 proposes technology for eliminating color differences due to the order in which the colorant is deposited in bidirectional printing, and describes a process using two lookup tables, a color process lookup table (LUT) for the outbound pass, and a color process lookup table (LUT for the return pass.
JP-A-2004-34435 describes technology for matching with high precision the color tone of images recorded on the outbound pass and the color tone of images recorded on the return pass, and describes forming the return image of each ejection pressure proportionally to the outbound image.
Furthermore, JP-A-2003-25613 describes determining, based on the name of the print medium, whether the print medium to be printed on absorbs ink easily or resists ink absorption, determines, from the image information of the CMYK image data and the scanning pattern, the degree of change in the hue due to bidirectional recording of the pixels, and changes the density of C, M, and Y to reduce the output density of hues in the input image data with a large change in hue, and increase the output density of hues with a small change in hue.